1. Field of the Invention
The invention relates to a device for thermal energy injection, in particular for printing formes imaged by means of a digital imaging system, in particular by means of a laser-induced thermotransfer method.
2. Description of the Related Art
An imaging system of this type for digitally inscribable and re-erasable offset printing formes, in which fixing, that is to say homogeneous heating, of the printing-forme surfaces is carried out, is known from EP 0 693 371 B1.
The imaging unit operates on the outer-drum principle, in which a narrow ink ribbon similar to a typewriter ink ribbon is guided past the rapidly rotating impression cylinder, whilst a laser beam transfers the layer of the ink ribbon onto the impression cylinder by means of heat. This results in the ink-carrying image parts.
After imaging from the digital data stock, the printing forme is fixed for greater durability, that is to say the ink-carrying image parts are anchored to the printing forme.
After an order has been printed out, the rubber blankets are washed, and the printing forme is freed of ink residues and of the printing layer with the aid of a nonwoven and special washing agents. A bare cylinder is then available again for the next imaging operation.
In the fixing step, the imaged printing forme is heated to a surface temperature of between 170xc2x0 C. and 210xc2x0 C. by a dryer in the form of a hot-air blower which can be thrown onto the rotating printing forme, in particular a printing forme sleeve, and can be thrown off the latter again.
Although this fixing by hot gas is independent of the material of the printing forme, introducing hot gases into the printing machine in this way nevertheless presents problems and is undesirable.
The object of the present invention is to provide for rotating printing formes consisting of a material into which energy can be effectively introduced, that is to say which has a high ohmic resistance and is magnetic, to provide, within the printing machine, a device for thermal energy injection, in which hot gas does not have to be used and by means of which energy injection capable of being controlled with high accuracy in terms of time is possible.
This object is achieved by means for injecting thermal energy inductively into the printing forme therewith to effect an inductive fixing of said data to said printing forme. The means for injecting thermal energy inductively includes at least one inductor and a high-frequency component electrically connected with the inductor to form a reasonant circuit therewith. A power supply unit is connected to the high-frequency component with a supply line.
Together with all the other steps, such as hydrophiling, imaging and erasing, the fixing operation can, of course, also be executed within the printing machine, without the forme cylinder or printing forme being removed.
Since the fixing operation is carried out by means for the inductive fixing of the image information on the rotating printing forme consisting of a material suitable for induction heating, particularly advantageously in the medium-frequency range of 100-500 kHz, a time saving of up to 60% can be achieved, as compared with the hot-gas fixing method described in the prior art.
The invention also provides that by, for example, duplication of inductor loops, the number of regions of energy injection can be increased and, consequently, the active time of the fixing operation reduced, thus resulting, in turn, in an efficiency higher than that of the hot-gas fixing operation and therefore a marked energy saving.
In energy injection by induction, heating within the material, here the image information (thermomaterial), is brought about by means of a high-frequency alternating current. As is known, due to the so-called skin effect, heating can be applied either to a high degree onto the surface by means of high frequencies or else further into the material by means of lower frequencies. At the same time, energy injection is restricted in a punctiform manner, which, as stated, is particularly advantageous in terms of energy consumption.
Although induction heating depends on the material, it may nevertheless be employed in a focussed manner, since action having pinpoint accuracy can be achieved below the inductor loops.
The device according to the invention is therefore not highly suitable for specific printing formes (for example, those consisting of copper since the ohmic resistance is very low, or of aluminium), but it can be used with high efficiency for a large number of printing formes conventionally employed.
Suitable printing formes and their materials are also described extensively in EP 0 693 371 B1.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.